An electret power generating apparatus comprising a first substrate including a first electrode and a second substrate including a second electrode arranged to be opposed to the first electrode is known in general.
A conventional electret power generating apparatus disclosed in National Patent Publication Gazette No. 2005-529574 comprises a movable portion provided with an electrode having conductivity and a fixed portion provided with an electrode consisting of an electret material where charges are held. The electrodes provided on the movable portion and the fixed portion respectively are arranged to be opposed to each other, while the movable portion is supported to be held between spring members. The apparatus is so formed as to generate power by generating electrostatic induction between the opposed electrodes when the movable portion vibrates in a parallel direction with respect to the fixed portion.
In the conventional electret power generating apparatus disclosed in the aforementioned National Patent Publication Gazette No. 2005-529574, however, the movable portion is supported by the spring members and hence may move not only in a direction parallel to a surface on which the electrode is arranged but also in an orthogonal direction. In this case, the distance between the electrodes provided on the movable portion and the fixed portion respectively cannot be regularly kept constant, and hence there is such a problem that an electrostatic force acting between the electrodes changes and the quantity of power generation obtained in power generation becomes unstable.